var dustObj = function() {

	this.x = [];
	this.y = [];
	this.amp = [];
	this.N = [];
	this.alpha;
}

dustObj.prototype.num = 30;

dustObj.prototype.init = function() {
	for(var i=0; i<this.num; i++) {
		this.x[i] = Math.random() * canWidth;
		this.y[i] = Math.random() * canHeight;
		this.amp[i] = 20 + Math.random() * 15;
		this.N[i] = Math.floor(Math.random() * 7);
	}

	this.alpha = 0;
}

dustObj.prototype.draw = function() {
	this.alpha += deltaTime * 0.0008;
	var l = Math.sin(this.alpha);
	for(var i=0; i<this.num; i++) {
		var no = this.N[i];
		ctx1.drawImage(dustPic[no],this.x[i] + this.amp[i] * l,this.y[i]);
	}
}